Show Visualizers Error "could not load this custom viewer"

When I try to inspect DataSet by standard DataSet visualizer I see this error "could not load this custom viewer". I wrote simple dataset visualizer, but error throws anyway too.

On other computers with the same configuration visualizer show without any errors.

OS: Windows 7 x86 (Release)

VS: Visual Studio 2010 RC

has somebody any ideas?

I reinstall VS with no effect.

I found workaround! I changed source code of DevExpress module and recompile it. After that I undo parameter to NetFx40_LegacySecurityPolicy enabled="false", and enjoy. :)

File is "%DeveloperExpress.NET%\Sources\DevExpress.Data\Utils\Security.cs"

using System;
using System.Security;
using System.Security.Permissions;
namespace DevExpress.Data.Helpers {
    public static class SecurityHelper {
        public static bool IsPartialTrust {
            get {
                return !IsPermissionGranted(new ReflectionPermission(ReflectionPermissionFlag.MemberAccess));
            }
        }
        public static bool IsPermissionGranted(IPermission permission) {
            bool result = true;
/* (changed by Lion)
            try {
                PermissionSet ps = SecurityManager.ResolvePolicy((System.Security.Policy.Evidence)null);
                ps = ps.Copy();
                ps.AddPermission(permission);
                ps.Demand();
            }
            catch (SecurityException) {
                result = false;
            }
*/
            return result;
        }
    }
}